Filter media surface modification for enhanced sealing and apparatus utilizing the same

ABSTRACT

A novel surface treatment is provided for portions of filter media coming in contact with the filter media holder, such as a filter housing. In certain applications, the treatment is also applied to the filter media holder, depending on the application. Filter media having at least two distinct surface property modifications are provided in liquid filtration applications to enhance the performance of a filtration system, reduce the cost of the system, provide a visual means of detecting fluid bypass, and minimize fluid hold-up volume within the filter media, all with substantially no loss of performance performances parameters, even in steam sterilization applications.

CROSS-REFERENCE TO RELATED APPLICATION

This application is claiming the benefit, Under 35 U.S.C. 119(e), of theprovisional application filed on Nov. 30, 2001, under 35 U.S.C. 111(b),which was granted Ser. No. 60/334,256. The provisional application60/334,256 is hereby incorporated by reference. The provisionalapplication 60/334,256 is as of the date of filing of the presentapplication.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a filter media with at least tworegions with distinct media properties that result in an enhancedsealing of filter media between individual layers or between the filtermedia and a sealing means. More specifically, the present inventionrelates to a surface property modification of filter media and/or asealing surface to enhance the sealing of the filter media withinvarious filter housings. More particularly, the present inventionrelates to a surface property modification which repels liquid at thepoints of contact between the porous filter material and the sealingsurfaces of the filter housing. Most particularly, the present inventionrelates to an improved filter medium that results in an improved sealingof filters and provides means for fluid-gas transfer

2. Discussion of the Related Art

It is well known in the art that one of the most important aspects of afilter design, especially in critical fluid filter applications such asmedical products and semi-conductor applications, is the prevention offilter failure.

In critical applications, even minor amounts of fluid bypass result in anonconforming fluid for the application at hand. Therefore, providinggood sealing between various components of a filter or filtration systemis critical.

One of the most common, but not the most reliable, sealing mechanisms todate is a pinch seal. In a typical pinch seal the filter media issqueezed between two sealing surfaces. In a typical seal, specialattention must be focused upon the amount of pressure imposed on thefilter media to assure proper sealing and to minimize the possibility offluid bypass. Special attention must be focused upon the structuralproperties of the media and its capability to handle the stress causedby the pinch seal. Typically, in a pinch seal, a designer would like toprovide a maximum pressure at the seal without compromising thestability of the filter structure. The higher the pressure at thesealing surface, the higher the compression of the media at point ofcontact. Typically, this can result in a reduced pore size in theaffected area, and also reduce the gap or pore size between the filtermedia and the sealing surface. This prevents fluid flow past the pinchseal as long as the pore size is small enough to block flow. Another wayto stop flow past the seal is to block the pores proximate the seal withpotting compound.

The present invention provides a better seal without the aforementionedproblems. This is accomplished by making the seal material non-wettingto the fluid being filtered and, thereby, providing a liquid repellantseal. More specifically, a liquid repellant porous seal with a liquidwetting filter area. The wetability (fluid wetting properties) of theseal may be adjusted by methods known in the art. The present inventionprovides a differential wetability at the sealing surface.

The present invention teaches that the wetability of the seal may bedecreased to prevent fluid bypass past the seal. At the same time, themain filter area is desired to be fluid wettable, especially for fluidfilter applications, to provide fast priming times. In gravity feedsystems or low pressure applications, the wetability of the filtermedium is important as there is a minimum breakthrough pressure requiredto start fluid flow through a filter. The breakthrough pressuredecreases with increased wetability. Therefore, the present inventionprovides a differential wetability of the filter media at the sealingsurface. Also, it is noted that the surface property of the sealingsurfaces, such as the housing, may be changed to enhance the seal.

In general, the wetability of a porous material depends on a number ofparameters, including pore size and surface properties of the materialinvolved. In addition, there will be a number of other advantages to thepresent invention that will be apparent from the descriptions providedand the applications shown.

Present day filter media, whether in the form of flat sheets of variousshapes, such as circles, ovals, or other desired shapes, or in tubularform, are generally homogeneous throughout, and consist entirely offilter media without any treatment to the sealing regions to enhancesealing. This produces problems in the art. With filter media sheets,there tends to be leakage past the commonly used pinch seal, unless thisseal is carefully designed. Such attention to the seal increases thecost of the filter housing holding the media, may result in additionalcomponents, and an increase in final product weight, to effect a properseal. Sometimes, adhesives or other agents are needed to effect any sealat all. Also, since the pinch seal is typically wetted by the fluid,there is no possibility of a visual aide in discerning if the seal isadequate and the fluid being filtered is not bypassing the seal. Avisual aide in detecting fluid bypass may provide an opportunity to savethe fluid such that it may be processed in a single pass.

The same problems occur with tubular filters when attempting to provideeffective seals at or near the ends of the filter tubes. The prior artis replete with special types of end caps and housing modificationsdesigned to effectuate the seal between the tubular filter media, whichis usually made of randomly oriented fibers (particles), and an end capand/or housing. Again, these measures increase costs for the filterproducts. Thus, those skilled in the filter art continued to search fora better method of sealing filter media within filter housings.

In critical applications adhesive may be used to increase thereliability of the filter seal by typically filing the gaps or poresbetween the sealing surface and the media. The adhesive may be surfaceloaded in the area of the seal, or the adhesive may be presentthroughout the depth of the filter media for added protection againstfluid bypass.

The addition of adhesive, typically provides a barrier to fluid bypasspast the sealing surface. But in addition, it may provide addedcomplications in certain applications. These include separation ofvarious components of the adhesive, which may result in physicalproperty changes in the seal such as bio-compatibility, thermalstability and chemical compatibility, decreased process time as theadhesive is typically thickened to control wicking of the adhesive intothe filter media, and reduced versatility of the adhesive and/or themedia as each application needs to be considered on a case by case basisto ensure a proper seal. Also, it is important for the adhesive to bondproperly to the housing to provide an adequate seal. Delamination of theadhesive between the various components may result in fluid bypass.

If the adhesive is a multi-component, the various components of theadhesive may separate due to the capillary forces present in the filtermedia and may compromise the properties of the adhesive and the seal.Also, in certain instances this may result in bio-compatibility and/orleachability issues.

In addition, adhesives may have different physical properties than thefilter media and the housing. Certain environmental conditions mayresult in a compromise of the seal. An example of such instance may bewhen the thermal expansion property of adhesives may not match that ofthe housing. Therefore, certain thermal fluctuations (such as those seenin typical medical applications requiring autoclaving) may result in acompromising of the seal. This is especially important in medicalapplications requiring autoclaved parts or heat or steam sterilization.

The present invention provides novel solutions and enhancements to theseproblems in the prior art. The present invention will describe ahydrophobic (hydrophobic in the context of this application issynonymous with liquid repellant) barrier that may be used inconjunction with the use of adhesives. The hydrophobic barrier willprovide a restriction to the wicking of adhesive past a desired point.In addition, it provides a general means of treating media that may beused with various adhesives. Currently, the properties of the filtermedia and the adhesive are chosen such as to control the wicking of theadhesive. The present invention provides a novel concept, a barrier,such that these factors are not as important. The media may be used witha various adhesives, and one adhesive may be used with a variety ofmedia. The barrier also provides a clear and distinct area where theadhesive will be present. Advantages include reduced variation in filterproperties, such as flow rate, efficiency and capacity, as the usablefilter area is clearly defined by the barrier.

The present invention also provides novel means to provide an enhancedsealing mechanism for filtration and separation applications. One novelconcept provides a porous seal with enhanced seals to decreasepossibility of bypass. The novel concept minimizes fluid hold-up volumewithin a filter and enables greater fluid recovery. It also decreasescost of the filtration system by the possibility of eliminatingcomponents such as adhesive, and also reduces the weight of the filterby providing a porous structure seal through elimination or minimizationof adhesive usage. In special configurations to be described, thepresent invention provides an integral venting means within the filterthat is an integral part of the sealing means.

Further, the present invention describes a novel concept that providesenhanced sealing of filter by providing a barrier to fluids. The barrierprovides a means to prevent fluid contact across a pinch seal. In its'simplest form, the barrier provides a definite and clear barrier againstfluid wicking or fluid migration. One of the advantages of this novelconcept is that it prevents separation of multi-component adhesives. Inaddition, it broadens the selection criteria for filter media and/oradhesive. This is due to the fact that the barrier provides a broaderrange of adhesives that may be used with a given filter media structure.The influence of adhesive properties such as surface tension, viscosity,and gel time are minimized and, as such, provides a greater flexibilityin the production of various filters. Also, the barrier enablescombining a number of filters into a single filter housing. The singlehousing concept reduces the number of components and provides overallcost savings.

Providing multiple filters in a single housing with integral non-wettingbarrier enables a number of novel concepts for filtration and separationsystems. Fluids may be processed side by side. The barrier may bepenetrated at elevated pressures providing unique separation and mixingapplications. For example, the filter may be subjected to sufficientpositive and negative pressure to drive fluid across the barrier. Thepressure may be applied by various means known in the art such ascentrifugation, infusion pumps, syringe, etc. A number of applicationswill be described in this application to demonstrate the novelty of thisconcept.

Other advantages of the present invention will be apparent from thedescription hereby provided.

SUMMARY OF THE INVENTION

The problems in the art are solved by the present invention by providinga novel surface treatment for portions of the filter media coming incontact with the filter media holder, such as a filter housing.

There are various methods known in the art for producing surface(material) property modifications. These include chemical, mechanical,plasma, corona and heat (flame) treatment. Preferred chemical treatmentsfor hydrophobic applications are fluorinated, siliconized,fluorosilicon, polyolefin polymers which result in reducing the criticalwetting surface tension of the material.

In general, most polymers have a low surface tension and may be used ascoatings to modify the CWST of a material. Due to their low surfacetension they are typically used to provide a liquid repellant region.Preferred chemical treatments for hydrophilic applications includepolymers with a hydroxyl functional group such as Poly-vinyl Alcohol andcellulose, and a functionalized cellulose group such as celluloseacetate and ethyl cellulose, carboxylic acid functional group, aminefunctional group, sulfonic acid functional group. It should be notedthat chemical treatments in varying quantity may be applied to variousregions to provide distinct wetting properties. For example, the pinchseal region may be made more hydrophobic than the filtering region byapplying a larger quantity of the hydrophobic binder to the pinchregion. In general the regions may have varying compositions to providefor the desired functions pointed out in the invention.

In certain applications, an internal vent is provided by means of anovel surface treatment to provide for faster priming of the filterwithout entrapping gas upstream of the filter media, which may adverselyeffect the filtration process (increase filtration time, decreaseefficiency).

The present invention provides for a porous media with at least twodistinct surface property modifications in liquid filtrationapplications to enhance the performance of the filtration system, reducethe cost of the system, and provide a visual means of detecting possiblefluid bypass.

The present invention is related to, but not limited to, filter media,fluid processing, gas venting, gas transfer, and fluid transfer. A meansof providing a preferential fluid flow within a filter by liquiphobic(liquid repellant) or liquiphilic (liquid wetting) treatment of a porousmedium is disclosed.

The present invention is most suited for, and related to, pinch sealswhere a porous media is sealed within a housing by pinching or flatgasket sealing of media within the housing. This method is commonly usedin price/cost sensitive applications. One of the drawbacks of pinchsealing has been the possibility of fluid bypass.

One of the possibilities of bypass is due to preferential permeabilityor wetability of the media in the cross-flow direction. This situationis especially important with thick filter media over sealing surfacelength seals. The present invention reduces the risk of such bypass.

These benefits are achieved through the aforementioned surface propertymodification of the filter media, which is based on the relationshipbetween the critical wetting surface tension (CWST) of the filter mediabeing used, and the surface tension of the fluid being filtered.

For the purposes of the present application, the definition of the CWSTof the media is not the one generally known in the art from U.S. Pat.No. 4,880,548 ('548), the specification of which is incorporated hereinby reference. The ('548) patent defines a media to be wetting if itabsorbs at least 9 out of the 10 test drops after 10 to 11 minutes atatmospheric pressure. Instead, it is a use based CWST.

In the present application the CWST of the filter media will bedetermined based on the particular application or intended use. As inthe ('548) patent, a CWST for a series of materials can be determined,but they will all relate to a particular use or application, and may, ormay not be relevant to any other use or application.

For example, if a quick priming filter element is desired, one whichwould not entrap gas in the upstream chamber for two minutes while theupstream chamber fills, and the filter inlet pressure is 40″ of fluidcolumn, a satisfactory filter media would be one in which at least aportion of the filter media remains unwetted and capable of ventingentrapped gas until the upstream chamber is filled. This requirestesting of the filter media with a series of standard liquids withvarying surface tensions in a sequential manner under test conditionswhich simulate actual desired operating conditions. This may be done byplacing a number of drops (for example 10) or columns of test fluid (ifunder differential pressure) on representative portions of porous media,and allowing these to stand for a desired time (in this example twominutes). Observation is made after a desired time (two minutes).Wetting is defined as absorption or wetting of the porous media by atleast nine of the ten drops or a reduction in the volume of nine out often columns by the equivalent of one drop per column within the desiredtime. Non-wetting is defined as the retention of a negative angle ofcontact (for drops), or a substantial retention of volume (for columns).For drops, nine out of ten drops must retain a negative angle ofcontact. For columns there should be substantially no loss of volume dueto absorption by the media (less than one drop).

Testing is continued using liquids of successively higher or lowersurface tension, until a pair has been identified, one wetting and onenon-wetting, which are the most closely spaced in surface tension. TheCWST according to the present application is then in that range. Forconvenience, the average of the two surface tensions is used as a singlenumber to identify the CWST for the particular application.

Furthermore, the media in the above example does not need to benon-wetting for any more than the two minutes the fluid takes to fillthe chamber and the gas to vent (perform its intended function). Themedia may be wetting after the time it takes to perform its intendedfunction.

Any further references to CWST in the present application refer to theCWST as defined above.

From this definition, and knowledge in the art, it can be seen that ifthe surface tension (ST) of the fluid is less than the CWST of thefilter media, then the fluid will wet the filter media, and the fluidbeing filtered will flow through the media. The greater the differencebetween the ST and the CWST, the faster the wetting or priming of thefilter media, and the faster the fluid will begin to flow through thefilter. Conversely, the closer the ST of the fluid being filtered is tothe CWST of the filter media, the longer the priming time of the filtermedia. If the ST of the fluid being filtered is greater than the CWST ofthe filter media, the fluid being filtered will simply bead up on thefilter media, and no flow will take place.

Using the above relationship between the ST of the fluid being filtered,and the CWST of the media being used, a surface property modificationmay be performed on the filter media by treatments known in the art suchthat liquids are repelled at the points of contact between the porousmaterial and the sealing surfaces. For example, if the filter media isliquid wetting (ST of fluid<CWST of media) a portion of the filtermedia, most preferably the portion which will be in contact with thesealing surface, is treated such that it becomes liquid repellant (ST offluid>CWST of media). It is also advantageous if the entire, or at leasta portion of, the sealing surface of the housing which will be incontact with the treated porous media would also be liquid repellant.This may occur because of the material of which the housing is made, orby treating the surface(s) of the housing which are to contact thefilter media.

The invention is not limited to surface treatment modification as thefilter media may be a composite with appropriate wetting characteristicsprovided by methods well known in the art.

The liquid repellant porous media will result in a higher than normalliquid breakthrough pressure compared to a non-treated media of the samestructure. Also if the porous media is liquid repellant throughout itsdepth, the fluid will not advance into the sealed portion, therebyreducing possible liquid holdup within the liquid repellant section ofthe porous media.

The present invention is well suited for low pressure applications, suchas gravity feed systems. An important feature of the present inventionis the creation of a fluid barrier that prevents liquid breakthroughpast the sealing surface. Due to the low fluid pressure of such systems,this may be accomplished by surface modification of the porous materialor media. For a liquid wetting filter media, the CWST of the media atthe seal is reduced, so that the CWST of the media is less than the STof the fluid being filtered, and therefore, the media will be liquidrepellant at the seal.

For a liquid repellant material, the surface tension of the material atthe seal may be increased further, to provide enhanced sealing.

Likewise, the central portions of the filter media may be treated toincrease or decrease how fast wetting of the media takes place, i.e.,how fast priming occurs. If a liquid wetting filter media is being used,the central portion may be treated to increase the CWST thereof, andmake the media more liquid wetting than otherwise. This may beadvantageous where it is desired to use a less costly media which is notparticularly fast priming, but treatment in the above manner can make itprime as fast as a more costly material. Conversely, one media may bedesirable for a particular application, but primes too fast. Treatmentin the above manner can slow the priming time. Other advantageousapplications are well within the scope of the present invention.

In one embodiment of the present invention, a flat sheet of a filtermedia made of a liquid wetting material is treated about the edgeregions thereof so that the CWST of the material at the seal is reducedto a value less than the surface tension of the fluid being filtered, sothat the material at the sealing surface is, in effect, liquidrepellant.

In another embodiment of the present invention, a flat sheet of filtermedia made of a fluid repellant material is treated about its interiorregions such that the CWST of the material at the interior regions isincreased.

In a further embodiment of the present invention, a tubular filter madeof a liquid wetting material or media is treated at its' sealingsurfaces such that the CWST of the material at the sealing surfaces isreduced to a value less than the ST of the fluid being filtered, andthus, is liquid repellant at the sealing surfaces.

In yet another embodiment of the present invention, a filter media in atubular configuration is made of a fluid repellant material and treatedat its' interior such that it is liquid wetting in the interior regions.

In a still further embodiment of the present invention, a filter mediaholder is provided for use with the improved filter media of the presentinvention such that a visual indication of fluid bypass of the filtermedia is easily provided.

In another modification of the present invention, a flat sheet of filtermedia (single or multi-layer composition) made of a liquid wettingmaterial has an annular portion near the edge of the filter materialtreated to reduce the CWST of the material at the sealing region of thefilter sufficiently such that the media is liquid repellant.

In a still further embodiment of the present invention, a flat sheet offilter media of a predetermined shape, and made of a fluid repellantmaterial, has an annular portion proximate the sealing region of thefilter material treated such that the CWST of the material is decreasedin the annular region.

Thus, it an object of the present invention to provide a surfacetreatment modification for a filter media which will enhance the sealingof the filter media within a filter holder or housing, or between filtermedia layers.

Another object of the present invention is to provide enhanced sealingbetween a porous media and a filter housing without the use ofadhesives.

Another object of the present invention is to provide a filter mediawhich has been surface treated and mounted in a filter housing toprovide an effective seal with a reduced number of components.

A still further object of the present invention is to provide animproved surface treated filter media which achieves an effective seal,and is lighter in weight for the same application, than the known filtermedia.

Another object of the present invention is to provide a filter mediahaving a liquid repellant porous sealing region and a liquid wettingfilter area with minimum fluid hold-up volume within the filter media.

Another object of the present invention is to provide an improved filterhousing for use with the surface treated filter media which provides avisible means of detecting fluid bypass, thus providing a visual meansof detecting filter or housing failure.

Another object of the present invention is to provide a novel filterhousing which, when used in combination with the surface treated filtermedia of the present invention, increases fluid recovery.

Another object of the present invention is to provide a filter mediathat has at least two distinct surface properties proximate to thesealing surface.

Another object of the present invention is to provide a filter mediathat provides a barrier to fluid migration past a sealing surface.

Another object of the present invention is to provide an improvedadhesive bounded seal with a precise adhesive/non-adhesive boundary.

Another objective of the present invention is to provide a filter media(single or multi-layer) that prevents separation of multi-componentfluid mixtures.

Another object of the present invention is to provide a filter media(single or multi-layer) that prevents the separation of multi-componentadhesive at the sealing surface.

Another objective of the present invention is provide a non-wettingregion proximate to the sealing surface which may be breached underelevated differential pressure across the seal.

Another object of the present invention is to provide a consolidatedfilter element with porous separating barriers that do not have a liquidcommunication means.

Another object of the present invention is to provide a liquid barrieracross a sealing means.

Another object of the present invention is to decrease liquid hold-upvolume within a sealing region.

Another object of the present invention is to provide an integralventing means integral within the filter media.

Another object of the present invention is to provide a venting meansintegral with an enhanced sealing means.

Another object of the present invention is to provide a filter withmultiple separated compartments.

Another object of the present invention is to provide a platform formixing, transporting, separating fluid(s) across a liquid repellantporous partition.

Further objects and advantages of the present invention will be apparentfrom the following description and appended claims, reference being madeto the accompanying drawings forming a part of the specification whereinlike reference characters designate corresponding parts in the severalviews. It should be noted that although two-dimensional filter mediaconfigurations are discussed within this application, other filter mediaconfigurations, such as corrugations, domed, tubular or, in general,three-dimensional configurations, are within the scope of thisinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a known filter media of circular shape.

FIG. 2 is a diagrammatic sectional view, showing a representative filterholder holding the filter media of FIG. 1.

FIG. 3 is a perspective view of a known filter media in tubular form.

FIG. 4 is a diagrammatic representation of one common way of sealing thefilter media shown in FIG. 3 in a filter housing.

FIG. 5 is a perspective view of a construction embodying the presentinvention.

FIG. 6 is a sectional view, taken in the direction of the arrows, alongthe section line 6-6 of FIG. 5.

FIG. 7 is a sectional view, in large part similar to FIG. 6, but showinga modification of the present invention.

FIG. 7A is a sectional, elevational, view showing a modification of theconstruction shown in FIG. 7.

FIG. 7B is a sectional, elevational, view showing a further modificationof the construction shown in FIG. 7.

FIG. 7C is a sectional, elevational, view showing a further modificationof the construction shown in FIG. 7.

FIG. 8 is a diagrammatic sectional view, showing the construction ofFIG. 5 mounted in a novel filter housing.

FIG. 9 is a perspective view showing a filter media constructionembodying a further modification of the present invention.

FIG. 10 is a sectional view, taken in the direction of the arrows, alongthe section line 10-10 of FIG. 9.

FIG. 11 is a sectional view, in large part similar to FIG. 10, showing afurther modification of the present invention.

FIG. 11A is a sectional, elevational, view showing a modification of theconstruction shown in FIG. 11.

FIG. 11B is a sectional, elevational, view showing a furthermodification of the construction shown in FIG. 11.

FIG. 11C is a sectional, elevational, view showing a furthermodification of the construction shown in FIG. 11.

FIG. 12 is a diagrammatic sectional view, showing the construction ofFIG. 9 mounted in a novel filter housing.

FIG. 13 is a perspective view of a further modification of the presentinvention wherein a vent is added to the construction of FIG. 9.

FIG. 14 is a sectional view, taken in the direction of the arrows, alongthe section line 14-14 of FIG. 13.

FIG. 15 is a sectional view, in large part similar to FIG. 14, showing afurther modification of the present invention.

FIG. 15A is a sectional, elevational, view showing a modification of theconstruction shown in FIG. 15.

FIG. 15B is a sectional, elevational, view showing a furthermodification of the construction shown in FIG. 15.

FIG. 16 is a diagrammatic sectional view, showing the construction ofFIG. 13 mounted within a novel filter housing.

FIG. 17 is an exploded perspective view of the construction shown inFIG. 16.

FIG. 18A is a perspective view, partly fragmented, showing a furthermodification of the present invention.

FIG. 18B is a perspective view, showing a further modification of thepresent invention.

FIG. 18C is a diagrammatic view of an improved filter housing embodyingthe present invention which can utilize the constructions shown in FIGS.18A and 18B.

FIG. 18D is a modification of the construction shown in FIG. C.

FIG. 18E is a view similar in part to FIG. 18D, but showing taperedwalls on the end cap illustrated which are designed to slightly “crush”the end of the filter tube when it is sealed in the filter housing ofFIG. 18C.

FIG. 18F is a view similar to FIG. 18E, but showing the filter tube ofFIG. 18E fully installed in the end cap, with the end of the filter tubeslightly “crushed”.

FIG. 18G is a view similar in part to FIG. 18 e, but showing the surfacetreatment only at the outer peripheral wall of the filter tube, andshowing only a tapered, outer peripheral wall on the end cap.

FIG. 18H is a view similar in part to FIG. 18E, but showing the surfacetreatment only at the inner peripheral wall of the filter tube, andshowing only a tapered, inner peripheral wall on the end cap.

FIG. 19 is a perspective view of a fluid filter construction embodyingthe present invention.

FIG. 20 is a front elevational view of the construction shown in FIG.19.

FIG. 21 is a sectional view, taken in the direction of the arrows, alongthe section line 21-21 of FIG. 20.

FIG. 22 is a perspective view, similar in part to FIG. 13, but showingthe addition of a top or upper vent.

FIG. 23 is a perspective view, similar in part to FIG. 22, but showingthe upper vent overlapping the surface treatment modification and beingconstructed of the same material.

FIG. 24 is a perspective view, similar in part to FIG. 22, but showingthe upper vent overlapping the surface treatment modification and beingconstructed of a different material.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1-2, a typical filter media 30 in a flat sheet formis shown. While the media is shown in a circular shape, the media may bein an oval, square, diamond or other desired shape. The filter media 30may be made of more than one layer, if desired.

A section taken through the filter media 30, such as shown in FIG. 2,reveals no distinct surface property variation proximal to the sealingsurface. Thus, nothing is found in the prior art filter media 30 itselfto aid in sealing it in a typical filter housing 31, such as isillustrated in FIG. 2.

The typical filter housing 31 will normally be of a shape complimentaryto the filter media 30, and designed to pinch seal the filter media 30between two halves of the filter housing. The filter housing 31 has afirst half or portion 32 having a first circular side wall 33, a firstupstanding peripheral wall 34 at the periphery thereof, and a second,inwardly spaced, peripheral upstanding wall 35 spaced inwardly apredetermined desired distance from the upstanding outer peripheral wall34. A first annular space 39 is formed between the sidewalls (34,35). Anoutlet 36 is formed on the circular sidewall 33 for purposes to bedescribed.

A mating second half or portion 40 has a second circular sidewall 41, asecond upstanding peripheral wall 42, and a second, inwardly spaced,upstanding peripheral wall 43. The second upstanding peripheral wall 43is evenly spaced a predetermined distance from the second upstandingperipheral wall 42 to provide a second annular space 44.

The dimensions of the first filter portion 32 and the second filterportion 40 are chosen such that the inside diameter of the firstupstanding peripheral wall 34 is related in a predetermined, desired,manner to the outside diameter of the second upstanding peripheral wall42. Depending on how it is desired to fasten the first portion 32 andthe second filter portion 40, these dimensions may be chosen to providea loose fit, an adjacent fit, or an interference fit between the firsthalf 32 and the second half 40 of the filter housing 31.

To assemble the filter housing, the filter media 30 will be placed inthe filter housing 31. The filter media 30 preferably has a diametersubstantially equal to the inside diameter of the second upstandingperipheral wall 42. The filter media may be laid in the second filterportion 40 and, because the second inwardly spaced upstanding peripheralwall 43 is of a height less than the second upstanding peripheral wall42, the filter will lay on top of the second inwardly spaced peripheralwall 43.

The first or cover portion 32 of the filter housing 31 is then placedover the second filter portion 40. Since the diameters of the firstinwardly spaced peripheral upstanding wall 35 of the first filterportion 32, and the second inwardly spaced peripheral wall portion 43 ofthe second filter portion 40, have been chosen so that when the twohalves of the filter 31 are assembled they are substantially directlyopposite each other, and the height of the two walls have been carefullychosen, the filter media 30 will be “pinched” between the first inwardlyspaced peripheral upstanding wall 35 and the second inwardly spacedupstanding peripheral wall 43. The first portion 32 and the secondportion 40 of the filter housing 31 may then be bonded, sonic welded,adhesively or otherwise joined to each other. Fluid will come in theinlet 46, go through filter media 30, and exit out the outlet 36.

In some cases, to increase the reliability of the pinch seal, and reducefilter failure, adhesive is introduced to the first annular space 39 andthe second annular space 44 when the filter housing 31 is assembled.However, because of lack of surface treatment modification of the filtermedia 30, all of the aforementioned problems present in sealing flatsheet filter media may occur in one form or another in all the knownprior art filter housings.

Referring to FIGS. 3 and 4, a typical prior art tubular filter 50 isshown. The end 51 of the filter 50 shows no surface treatmentmodification, and typically none is found at either end of the tube 50.Therefore, the sealing problems discussed above in regard to flat filtermedia 30 are also present with tubular filters 50.

As shown in FIG. 4, tubular filter 50 is generally sealed in a filterhousing 47 between the filter head 48 and an end cap 49. Filter bowl 52seals the filter tube 50 within the filter housing 47.

Referring now FIGS. 5-8, there is shown a flat sheet of filter media 55embodying the construction of the present invention. The flat sheet ofmedia is shown in a circular shape, but may be of an oval, diamond,square or any other practical shape, and may be made of any mediamaterial. An annular shaped portion 56, proximate the edge 57 of thefilter media 55, has been treated such that the CWST of the media isless that the ST of the fluid being filtered, and therefore, the annularportion 56 of the filter media 55 is liquid repellant with respect tothe fluid being filtered. The interior 54 of the flat sheet 55 is lessliquid repellant and the annular shaped portion or perimeter 56 of thefilter media 55 is more liquid repellant.

As shown in FIG. 6, it is preferred that the liquid repellant portion 56extends entirely through the filter media 55. However, in someapplications, such as shown in FIGS. 7 and 13, it may be desired thatsome surfaces of each side of the flat sheet of media 55 be treated onlypart way through with liquid repellant to produce a first annular liquidrepellant portion 58 and a second annular liquid repellant portion 59.In such an application, the liquid repellant may extend only part waythrough the filter media 55, but not all the way through. While thisversion may be useful in some applications, it is not the most preferredembodiment, because the fluid being filtered may wick to the edge 57, orbeyond, resulting in possible fluid loss. However, it may be useful iffluid flow past the seal is desired without bypass at the sealingservice.

Modifications which prevent wicking to the edge are shown in FIGS.7A-7C. In FIG. 7A the filter media 55 has the annular or ring shapedtreated portion 56 in the form of an inwardly radially extendingU-shaped channel 56C. In FIG. 7B, it is shown as an outwardly radiallyextending U-shaped channel 56D. In FIG. 7C, the annular or ring shapedtreated portion 56 is in the form of a box channel 56E.

With reference to FIG. 8, there is shown a diagrammatic view of a novelcombination of a filter housing 60, and the flat sheet media 55, whichtogether increase efficiency, reduce hold-up volume, and achieve theaforementioned advantages. The filter media 55 is shown in a pinch sealarrangement between two halves (61,62) of the filter housing 60. Thefilter 60 consists of an inlet section 61 and an outlet section 62. Theinlet section 61 of filter 60 has an inlet 63 including port 63Acommunicating with a first passage 64, which is in fluid communicationwith a first or inlet chamber 65 through first port or outlet 64A.

A more detailed embodiment of a construction embodying the presentinvention is shown in FIGS. 19-21.

The filter 60, as aforementioned, includes an inlet section 61 which isbonded to an outlet section 62 by a seal 80. The seal 80 is preferablyan ultrasonic seal, and may be full, or partial. It can be understood bythose skilled in the art that other seals, such as heat seals, adhesiveseals, or any other air tight seal may be used.

Inlet section 61 includes a recessed top wall 91 and a downstanding sidewall 92 extending around the periphery of the top wall 91. A firstdownstanding peripheral ridge 93 extends around the periphery of thedownstanding sidewall 92 and forms a part of the mechanism which holdsthe filter element 55 in place, as will be more fully explainedhereinafter.

A first protuberance 95 extends from the recessed top wall 91 andcarries the inlet 63 and first passage 64 as previously described. Arecess 96 provided by the combination of the top surface of the top wall91, and peripheral side walls 97, almost completely surround theprotuberance 95.

A peripheral flange 98 extends from the peripheral side wall 97 andforms a groove 79 extending around the periphery of the inlet section 61of the filter 60. The groove 79 forms a portion of the construction bywhich the seal 80 between inlet section 61 and outlet section 62 of thefilter 60 is formed.

The shape of the outlet section 62 of the filter 60 is complimentary inshape to the inlet section 61 so that the inlet section 61 may act as aclosure to the outlet section 62, or vice versa. It can be easilyunderstood by those skilled in the art that the fluid filter 60 may beof any desired shape, such as the generally circular shape described, anoval shape, a diamond or any other desired shape. A filter media of anydesired shape may be placed in a housing of any desired shape and stillbe well within the scope of the present invention.

Similar to the inlet section 61, the outlet section 62 of the filter 60has a bottom wall 110 and an upstanding side wall 111. The top of theupstanding side wall 111 fits into the groove 79 in the inlet portion61, and is preferably sonically welded to form the seal 80. A secondprotuberance 114 is provided on the exterior portion of the bottom wall110 and carries the outlet 72.

A second downstanding peripheral ridge 115 complimentary in shape tofirst downstanding peripheral ridge 93 is provided. First downstandingperipheral ridge 93 and/or second downstanding peripheral ridge 115 maybe treated to increase or decrease their surface tension, if desired. Itshould be understood that the terms “upstanding peripheral ridge” and“down standing peripheral ridge” are used in the sense of describing apair of substantially opposed peripheral ridges which provide for apinch seal of a filter media. Other terms may be used to describe theseridges, such as “first” and “second”, or “left laterally extending” and“right laterally extending”, without departing from the scope and spiritof the present invention.

If desired, a plurality of ribs (not shown because they are well knownin the art) is provided on the interior surface(s) of the bottom wall110, and/or top wall 96, to help support the filter media 55, andprovide flow in the second or outlet chamber 68 of the filter 60. Inplacing such ribs, one needs to be concerned with the volume occupied bythe ribs.

The volume of the ribs [also] controls the amount of holdup volume ofthe filter. Typically, for many reasons, there are more ribs on thedownstream side of the filter. The main reasons include the fact thatthe upstream chamber may be typically drained, therefore, the hold upvolume on the downstream side becomes important. In addition, thedownstream side is typically cleaner, and particulate contamination andblockage of the ribs are not as important. Also, the higher rib countdownstream of the filter provides a better support. As fluid flows fromthe upstream side through the media, the fluid exerts a force on themedia. The media, if not well supported, may collapse within the ribs.This could adversely affect the filtration/separation process, includingimportant parameters such as process time, efficiency, and capacity.

When the outlet portion 62 and the inlet portion 61 are in matingrelationships, the first down standing ridge 93 and the seconddownstanding ridge 115 may be in a 180□ opposed relationship. Theseridges will provide the “pinch seals” indicated by the numeral 120.Since the media which has been treated extends radially inwardly of thepinch seal 120, a continuous vented area is provided in the filterchamber.

Returning now to the diagrammatic view of the filter shown in FIG. 8,the outlet section 62 of filter housing 60 has a second or outletchamber 68 which communicates with outlet 72 including port 72A throughsecond passageway 69. The filter element 55 separates the first or inletchamber 65 from the second or outlet chamber 68.

The flat sheet of media or filter element 55 may consist of one or morelayers, and be made of a wide variety of filter materials. Filterelement 55 is held in place in housing 60 between first annular ridge 66provided about the perimeter of the first or inlet chamber 65 formed inthe inlet section 61 of the filter housing 60, and the second annularridge 70 formed in the outlet section 62. Annular ridge 66 is providedto contact the media 55, and the second annular ridge 70 is chosen to bein a predetermined desired position opposite the first annular ridge 66,and pinch media 55 therebetween.

The first annular ridge 66 and the second annular ridge 70 arepreferably positioned so that they contact the treated or annular orring portion 56 of the filter media 55, which did not become wetted out,while the interior portion 54 did become wetted out. Any gas enteringthe filter housing through any means may pass through the non-wettedportion of the filter media, extending inwardly beyond ridges 66 and 70,into the downstream chamber 68, allowing fluid to drain from thedownstream lines (not shown), resulting in increased fluid recovery. Itis desirable that at least the portion of the filter housing adjacentthe perimeter or edge 57 of the media 55 be transparent or translucent,so that any fluid bypass past the first annular ridge and the secondannular ridge, 66 and 70 respectively, can easily be observed.

In the embodiment illustrated, the filter element 55 has a liquiphilic(liquid wetting) center 54, and a liquiphobic (liquid repellant)perimeter or edge 57 as previously described. In use, a biological fluidcontainer (not shown), such as a blood container, is placed in fluidcommunication with inlet port 63A. Similarly a biological fluidreceiving bag (not shown) is placed in fluid communication by means wellknown in the art with outlet port 72A. Fluid flow is initiated, andbiological fluid flows in the inlet port 63A through the first passage64, and through first port 64A into inlet chamber 65. In operation, asthe biological fluid enters the inlet chamber 65, the fluid may wickinto the filter element 55. The rate at which the biological fluid wicksinto the filter element 55 will depend on the properties of the filtermedia being chosen, and the biological fluid being filtered. Theseproperties include the pore size of the medium, the viscosity of thebiological fluid, the surface tension of the biological fluid and thecontact angle of the solid-liquid-gas interface. While the fluid levelis rising in the inlet chamber 65, any air entrapped in the inletchamber 65 is passing through a portion of the filter media 55 which hasnot yet wetted. The treated perimeter or edge 57 (liquid repellant)assures this possibility.

As the fluid level continues to rise in inlet chamber 65, at some pointthe biological filter element 55 will be sufficiently “wetted”, and thebiological fluid being filtered will “breakthrough” the filter element55, and start flowing into the outlet chamber 68. The fluid“breakthrough” depends on the pore size of the material, the surfacetension and the contact angle, as well as the pressure differentialacross the filter element 55.

The biological fluid, which has now started flowing though the filterelement 55, will first fill up outlet chamber 68, and when outletchamber 68 is sufficiently full, the biological fluid being filteredwill enter second passageway 69 and pass into the biological fluidreceiving container (not shown) through outlet 72.

Due to the pressure differential across the filter element 55, thebiological fluid continues to flow up into second passage 69. Eventuallyall of the biological fluid will be drained from the biological fluidcontainer and will have flowed through passage 64, in the presence ofexcess gas intended to maximize fluid recovery. It is at this point thatone of the advantages of the liquid repellant portion being added to thefilter media 55 clearly shows.

In a prior art construction, while all of the fluid flows through thefilter media 55 into the downstream or outlet chamber 68, the downstreamchamber 68 and the downstream line (not shown) would remain full intypical low pressure applications, such as gravity feed systems, becausethe media remains saturated with fluid, due to inadequate pressuredifferential across the filter media to allow air to breakthrough themedia. Thus, residual fluid will remain in the filter media, downstreamchamber, and downstream lines resulting in a substantial hold-up volume.

The present invention, in addition to providing an enhanced sealingmechanism, provides a novel means to increase fluid recovery, andprovides a means to vent gas from the upstream chamber. This isaccomplished through providing a differential wetability of the filtermedia at or about the sealing interface between the filter media andits' sealing means. The liquid repellant section, which provided a meansto expel gas from the upstream chamber 65 to the downstream chamber 68at the onset of filter priming, will at the end of the filtrationprocess, as gas enters the upstream chamber 65, provides a means for gasto travel across the media through the liquid repellant portion to thedownstream chamber to recover fluid in the downstream line. The integralgas vent and enhanced sealing means provides fast priming of the filter,as the filter media may be liquid wetting. This integral sealing andvent prevents gas entrapment in the upstream chamber as the liquidrepellant portion provides a barrier to fluid and therefore providing aventing means as the upstream chamber is being filled. This is veryimportant since, in typical filter applications, as the fluid enters thefilter and is in contact with a filter media that is easily wetted bythe fluid, due to capillary forces, the fluid typically wicks in advanceof the upstream chamber fluid gas interface. Therefore, if there is noventing means, this will result in gas entrapment in the upstreamchamber. Therefore, in the prior art, most media are chosen such thatthe filter media is not easily wetted by the fluid such that air is nottrapped in the upstream chamber but at the same time not to be liquidrepellant to such an extent that no fluid passes through the filtermedia. Therefore, the present invention provides many benefits thatenhances the overall performance of the filter media. These include butare not limited to, the venting capability that prevents gas entrapmentin the upstream chamber, provides increased fluid recovery, and providesfast priming of the filter. Also it prevents reduced filter mediaperformance if a bubble of air is inadvertently introduced into thefilter. In addition, the present invention provides the filter designerwith a wide latitude in choosing the material for the filter media basedon the critical wetting surface tension (CWST) of the filter media whenused in comparison to the ST of the fluid to be filtered as shown by thefollowing examples.

EXAMPLE 1

In a design where the liquid repellant region extends beyond the pinchseal, such as shown for example in FIG. 8, a filter designer can choosethe CWST of the filter media in a very broad range. In the case wherethe designer selects the CWST of the filter media to be much greaterthan the ST of the fluid being filtered, the filter media will be veryhydrophilic (liquid wetting). The present example includes cases inwhich the liquid repellant region extends to cover the entire pinchseal, goes beyond the pinch seal towards the filter media edge, or fullyextends to the edge of the filter media.

Using the housing of FIG. 8, for example, as a fluid, preferably abiological fluid, enters the housing through the inlet section 61, itwill begin to fill the upstream chamber 65. As fluid fills the upstreamchamber 65, gas exits the housing through the portions of the filtermedia 55 that has not been wetted by the fluid, i.e., the annularportion 56. Since the filter media 55 has been chosen to be veryhydrophilic, the filter 55 is fast priming, while at the same time gasfreely passes through the annular portion 56, and vents out of the gaschamber continuously. Since the media and fluid properties are such thatno gas entrapment occurs, there is no need for a separate venting means.

The fluid will then continue to flow through the filter media 55 untilthe fluid entering the upstream chamber 65 is exhausted. Because of thevent provided by the treated annular portion 56 that is not wetted bythe fluid, and which extends inwardly beyond ridge 70, as gas enters theupstream chamber it will pass through non-wetted portion 56 and,therefore, in most cases fluid holdback will occur in the upstream anddownstream chambers (65, 68), while the inlet 64 and outlet 69 will beclear of fluid.

EXAMPLE 2

In a design where the liquid repellant region does not extend beyond thepinch seal, such as shown, for example, in FIG. 12, the filterdesigner's choices for the CWST of the filter media is limited incomparison to Example 1.

Since the non-wetting region does not extend inwardly beyond the pinchseal, it is preferable for the filter media to have a CWST such thatthere is no air entrapment in the upstream chamber as fluid first entersthe upstream chamber. [This limits the selection of the filter media ascompared to example 1.] Under optimal conditions for each example,filter media in example 1 will wet the surface faster than Example 2under similar conditions. The liquid repellant region, which provides animproved seal, is not wetted by the fluid throughout the filtrationprocess.

As noted previously, in this example, the liquid repellant portion 56 ofthe filter medium 55 does not extend past the pinch seal. Thereforethere is no gas venting means after gas enters the filter housing at theend of the filtration process. After the filtration process, fluidremains in the downstream chamber and downstream lines. The fluidretained in the downstream lines may be used for post evaluationpurposes. For example, in the blood banking industry typically thedownstream line is segmented, and the segments are used for variouspurposes, including quality assurance.

In this example, fluid enters the upstream chamber 65 and fills theupstream chamber. No air entrapment will occur in the upstream chamber65 as the filter media 55 is slow priming (not immediately wetted by thefluid). Once the fluid wets the filter media 55, and fills thedownstream chamber 68, fluid will enter the downstream line (not shown).At the end of the filtration process it is typically desired to filtersubstantially all of the fluid. Gas typically follows the fluid at theend of the filtration process. When the differential pressure across thefilter media 55 is lower than the pressure required to push air throughthe wetted filter media air does not pass through the filter media.Fluid drains from the upstream chamber 65 under differential pressureand substantially all the fluid is filtered. Gas is trapped in theupstream chamber and the downstream chamber, outlet 69, and thedownstream lines are filled with fluid. The fluid in the downstreamchamber 68 and line (not shown) may be used for post filtration samples.It is to be noted that Example 2 is most likely slower priming thanExample 1.

EXAMPLE 3

In this example the designer has again chosen a media wherein the CWSTof the media is greater or equal to the ST of the fluid being filteredsuch that no significant air entrapment would occur in absence ofdifferential surface tension property proximal to the sealing means. Inthis example, An annular portion 56, which includes a dome shaped, orother shaped, vent such as 76 shown in FIG. 13, has been treated to bemore liquid repellant than the filter media 55. Vent portion 76 acts asa vent after substantially all of the fluid is filtered and gassubstantially fills the upstream chamber 65. The liquid repellantregion, which is not wetted by the fluid, allows gas passage from theupstream chamber 65 into the downstream chamber 68 after substantiallyall the fluid is filtered. In order to recover as much of the fluid aspossible, the fluid repellant region 56 extends further inwardly at thebottom of the filter to form a gas vent 76. The gas passage through thisinwardly extending section allows the downstream lines to be drained. Byproviding a narrower gap and providing ribs in the downstream chamber itis possible to drain the downstream chamber completely.

EXAMPLE 4

Example 4 envisions the same choice by the designer as Example 3, withan additional liquid repellant region or top or upper vent 130 at thetop portion of the media, such as shown in FIG. 22. The media shown inFIG. 22 may be identical to the media shown in FIG. 13, except for theaddition of the additional liquid repellant region or upper vent 130.The upper vent 130 may be extending inwardly of the pinch seal to allowair to vent from the upstream chamber into the downstream chamber at theonset of the filtration process. This extra liquid repellant section orupper vent 130 is treated such that is not immediately wetted by thefluid. However, it is wetted during the filtration process. Thisadditional liquid repellant section 130 will provide faster priming ofthe filter housing. It will also provide a means for preventing gasentrapment in the upstream chamber 65 as the upstream chamber is filledat the start of the process. In addition, it will prevent gas passagethrough the section at the end of the process such that all fluid in theupstream chamber 65 may empty from the upstream chamber. Furtherpreferred embodiments of the present invention using these designconsiderations are discussed below.

Referring now to FIGS. 9-12, there is shown a modification of theinvention described in FIGS. 8-11 where the liquid repellant region doesnot extend inwardly past the sealing means. In this embodiment, anintegral gas vent is not present. A benefit of the present invention, asdescribed previously, is the enhanced sealing mechanism.

In this embodiment, in absence of a venting means, the filter media istypically chosen such that there is no significant gas entrapmentpresent in the upstream chamber at the onset of filtration. Due to alack of a venting means, at the end of the filtration process, as gasenters the upstream chamber, gas typically can not pass through thefilter, due to fact that the pressure differential required to pass gasthrough the wetted filter media exceeds that present as gas enters theupstream chamber. Therefore, gas fills the upstream chamber andsubstantially all fluid is filtered.

For ease in illustrating the various surface treatment modifications ofthe filter construction, the diagrammatic view of FIGS. 8, 12 and 16,rather than the more detailed filter housing construction views shown inFIGS. 19-21, will be used in the remainder of the application.

Referring to FIG. 9 there is shown a first modified sheet of flat media55A having a first modified or annular treated ring portion 56A spaced adistance “C” from the edge 57A of first modified filter element or sheetof media 55A. Used in conjunction with modified filter media 55A isfirst modified filter housing 60A, shown in FIG. 12. The construction offilter housing 60 and first modified filter housing 60A is substantiallyidentical except for the placement and dimensions of the secondupstanding ridge 115A formed on the outlet section 62A and the firstupstanding ridge 93A formed on the inlet section 61.

While first upstanding ridge 93A and second upstanding ridge 115A arestill in an opposed relationship, their width has been increased todimension D, which is wider than the width E of the first modifiedannular or ring portion 56A, and may begin at the outer periphery of thefirst modified annular or ring portion 56A and extend beyond the innerdiameter of the modified annular or ring portion 56A. Accordingly,dimension “D” may be greater than dimension “E”, and the first modifiedannular or ring portion 56A may be co-extensive with the outer diameterof the annular upstanding ridges (93A, 115A).

Referring to FIG. 11, it can be seen that in some instances the treatedannular portion 56A may not extend through the entire depth of thefilter media 55A but may instead have surface treated portions 56A onboth sides of the sheet of media 55A.

While this version may be useful in some applications, it is not themost preferred embodiment, because the fluid being filtered may wick tothe edge 57A, or beyond, resulting in possible fluid loss.

Modifications which prevent this are shown in FIGS. 11A-11C. In FIG. 11Athe first modified filter media 55A has the first modified annular orring shaped treated portion 56A in the form of an inwardly radiallyextending U-shaped channel 56F. In FIG. 11B, it is shown as an outwardlyradially extending U-shaped channel 56G. In FIG. 11C the first modifiedannular or ring shaped treated portion 56A is in the form of a boxchannel 56H.

A still further modification of the invention may be seen by referringto FIGS. 13-16. FIGS. 13 and 14 show a second modified filter media 55Bmounted in a second modified filter housing 60B (FIG. 16), which may besimilar to the first modified filter housing 60A shown in FIG. 12. Inthis instance, the dimensions C, D, and E may be equal and uniformaround the second modified media 55B, and may be identical to those ofthe first modified filter media 55A except where the filter vent 76 isprovided. The filter vent 76 is shown as a semi-circular shape, but maybe of any desired shape, and instead of being a width of dimension Dspaced a distance C from the edge, the filter vent is of a dimension Fwhich begins at the inner periphery of the second modified annular orring portion 56B and extends for a distance F, which brings a portion ofthe filter vent 76 above the first and second downstanding peripheralridges 93B and 115B respectively, which are pinch sealing the secondmodified filter element 55B in modified filter housing 60B.

In this modification of the invention, there is an extra passageway forair which extends above the ridges 93B, 115B pinching the secondmodified filter media 55B. As the fluid being processed passes throughthe inlet chamber 65B and through second modified media 55B, any airentrapped in the inlet chamber 65B will rise to the top of the inletchamber 65B. As the fluid continues to be filtered, the fluid level willdrop down to the bottom of the inlet chamber 65B, and any trapped aircan now pass through the filter vent 76, and up to the top of the inletchamber 65B. If a plurality of parallel ribs (not shown) are carefullyplaced downstream in the outlet chamber 68B this air will carry anyfluid remaining in the outlet chamber up and out through the outlet 72.Thus, in this modification of the invention, not only the inlet chamber65B, but the outlet chamber 68B, and the downstream line (not shown)will be empty, thus reducing hold back volume to a minimum.

Referring now to FIG. 15, a modification of the second modified filterelement 55B is shown where the second modified annular or ring portion56B does not extend for the entire depth of the second modified filtermedia 55B.

In FIG. 15, there is shown filter vent 76 having a front surface portion77, a rear surface portion 78, and a leg 83 connecting the front surfaceportion 77 and rear surface portion 78 proximate the middle thereof. Theleg 83 is needed for the air to pass between the front surface portion77 and rear surface portion 78, and may be placed in any desiredposition between the two. Even if placed below the fluid level in thefilter, the suction pressure is believed to be sufficient to cause theair remaining upstream after the filtering operation to pass through.While this is not a preferred embodiment because the fluid beingfiltered may wick to, and possibly past, the edge 57B, it may be usefulfor some applications.

Modifications which prevent this are shown in FIGS. 15A-15B. In FIG. 15Athe second modified filter media 55B has the second modified annular orring shaped treated portion 56B in the form of an inwardly radiallyextending U-shaped channel 56J. In FIG. 15B, it is shown as an outwardlyradially extending U-shaped channel 56K.

In FIG. 15A the leg 83 is shown connecting front surface portion 77 ofthe filter vent 76 and the rear surface portion 78 thereof at theirouter extremities in the form of a radially inwardly extending channel.In FIG. 15B the leg 83 is placed at the innermost possible position toconnect front surface portion 77 and rear surface portion 78 of filtervent 76. As explained hereinabove the leg 83 can be at the positionshown in FIG. 15A, the position shown in FIG. 15B, or any place inbetween and still perform satisfactorily.

With the foregoing explanation, additional benefits of the presentconstruction may be seen. When the flat sheet of media has the annularor ring portion 56 treated or present for the entire depth of the flatsheet of media as shown in FIG. 10, any fluid passing past thedownstanding peripheral ridges (93,115) is an indication of fluid bypassor filter failure, since a higher pressure is needed to bypass the pinchseals than if the treated annular or ring portion 56 were absent. Thus,if the filter housing (60,60A,60B) were transparent or translucent, atleast around the periphery thereof, any fluid which might flow past theannular or ring portion (56, 56A, 56B) could be easily observed by theuser of the filter housing (60,60A,60B) and the filter process could bestopped, and the fluid being filtered could be saved.

Referring now to FIGS. 18A-18H, it can be seen that the surfacetreatment modification of the present invention is not just useful withflat filter media or discs, but can also improve the sealingcapabilities of tubular filters as well. In FIG. 18A there is aperspective view of tubular filter 120 having an upper edge region 121Aproximate the upper end 121 of filter 120, and lower edge region 122Aproximate the lower end 122 of the filter 120 treated with the surfacetreatment modification of the present invention. The treated regions(121A, 122A) will preferably be of annular shape and may extend for theentire thickness of the filter tube, but may be of other shapes andcross sections if desired. For example, annular shaped treated regionsmay extend for a finite depth on the inside or outside of the tubularfilter 120.

By making the ends of the tubular filter 120 more liquid repellant, itis harder for liquid to bypass the ends of the filter tube when thefilter tube is held between a pair of end caps, as is typical in priorart filter housings. Thus, a tubular filter 120 having its ends 121,122, respectively treated with a liquid repellant is well within thescope of the present invention.

Referring now to FIG. 18B, there is shown a modification of theconstruction shown in FIG. 18A wherein the filter tube 120 has annularportions thereof (121A, 122B) treated with a surface treatmentmodification to be more liquid repellant than the remainder of thefilter tube 120. However, instead of being proximate the ends of thefilter tube (121,122), they are spaced a short, predetermined distance Xtherefrom. This will provide a mechanism for sealing the filter tube 120on its' outer and/or inner surface (120A,120B) instead of, or inaddition to, its' ends (121,122).

Referring now to FIG. 18C, there is shown a filter construction capableof accomplishing this. The filter construction shown in FIG. 18C may beidentical to the filter construction shown in FIG. 4, except that theend cap, now identified by the numeral 49A for the purpose of clarity,has been provided with a first or outer upstanding peripheral wall 49B,and a second or inner upstanding peripheral wall 49C spaced inwardly apredetermined distance from first or outer upstanding peripheral wall49B to create a pair of spaced walls between which the lower end of thefilter tube 120A can be sealed.

The spacing between the walls 49A, 49B should be such as to putsufficient pressure on the treated annular portion 122A to avoid fluidbypass.

The other end of the filter tube 120A may be sealed in a similar mannerby providing a modified upper end cap (not shown), or it may be sealedin a conventional manner.

Instead of a single treated region (121 a, 122A) being providedproximate upper and/or the lower ends (121,122) of the tubular filter120 being provided (as shown in FIG. 18A), a pair of treated annularregions (122C,122D) extending for a finite depth, less than thethickness of the tubular filter 120, may be provided proximate the upperand/or lower end of the tubular filter 120. This is shown on an enlargedscale in FIG. 18D.

Referring now to FIGS. 18E-18H, There are shown several modifications ofthe end cap 49A illustrated in FIGS. 18C and 18D. In FIG. 18E, there isillustrated a further modified end cap, now identified by the numeral150 for clarity. End cap 150, as can end cap 49A, may have an outerupstanding peripheral wall 150A (FIG. 18G), an inner upstandingperipheral wall 150B (FIG. 18H), or both FIGS. 18E, 18F). Also walls150A and 150B, as can walls 49B, 49C, can be in a concentric ornon-concentric orientation with each other, can be of any desiredheight, and can be placed anywhere on the end cap (150, 49A) dependingon the application.

Outer peripheral wall 150A may have a first slanted surface 160 providedon its inner portion 162. The angle which the slanted surface 160 makeswith the top surface 164 may vary depending on the application.

Likewise, the inner peripheral upstanding wall 150B may have a secondslanted surface 168 provided on its outer portion 170. A flat topsurface 175 may be provided as part of the outer peripheral wall 150Band/or the inner peripheral wall 150B if desired.

The slanted portions (160,168) are designed to push inwardly in on, andslightly crush the surface treated portions (122C, 122D) as pressure isapplied to the end cap 150 to seal the tubular filter 120 in a filterhousing, as shown in FIG. 18F.

The height of the walls (49B, 49C) (150A, 150B) should be sufficient sothat the inner wall (49C, 150B) and/or the outer wall (49B, 150A)contact at least a portion of the treated annular portion 122C and/or122D.

FIG. 18G shows a modification of the construction shown in FIG. 18Ewherein the end cap 150 has only an outer, upstanding, peripheral wall150A sealing against an outer surface treated portion 122C.

FIG. 18H shows a modification of the construction shown in FIG. 18Ewherein the end cap 150 has only an inner, upstanding, peripheral wall150B sealing against an inner surface treated portion 122C.

Referring to FIG. 22, there is shown a construction embodying thepresent invention, wherein a top or upper vent 130 is added to permit toallow air to vent from the upstream chamber into the downstream chamberat the onset of the filtration process for the purposes described above.The top or upper vent or upper surface treated area 130 can be treatedwith the same or different treatment as the vent 76.

FIG. 23 shows a construction similar to that shown in FIG. 22 whereinthe top or upper vent or upper surface treated area 130 overlaps theannular surface treated portion 56B, and is treated with the samesurface treatment modification.

FIG. 24 shows a construction similar to that shown in FIG. 22 whereinthe top or upper vent or upper surface treated area 130 overlaps theannular surface treated portion 56B, but is treated with a differentsurface treatment modification.

It may be desirable for some applications to have a top vent 130 asshown in FIGS. 22-24, without the bottom vent 76, and this is wellwithin the scope of the present invention.

The present invention is not limited to the circular discs or tubularfilters previously illustrated but may also be applied, as will beapparent, to other tubular or cylindrical elements that are pleated,formed and/or rolled. The shape of the treatment may vary to suit theapplicability of the filter design. For example as shown in FIGS. 5,9and 13, concentric treatments are shown, but the present inventionshould be understood not to be limited as such.

Further, there are various chemical treatments known in the art forproducing the surface treatment modifications. The preferred treatmentsfor such applications are fluorinated or siliconized polymers for liquidrepellant applications, and polyvinyl alcohol and cellulose acetate forliquid wetting applications. Other treatments will be apparent to thoseskilled in the art.

Many preferred embodiments of the present invention have been describedherein. The scope of the present invention is broad, and many moreembodiments of the invention can be developed using the teachingsherein, and these are well within the scope of the present invention.For example, with reference to FIGS. 8, 12, 16 and 21, the dimensionsshown are limited to the example in regard to which they discussed. Aslong as the hydrophobically treated portion of the media being held in apinch seal extends radially inwardly of the opposed upstanding wallsforming the pinch seal, a vented area will be formed. Therefore, forexample, in FIGS. 12 and 16, dimension D may be larger or smaller thandimension E, depending on the application, and be well within the scopeof the present invention.

Thus, by carefully considering the problems present with filteringfluids, a novel surface treatment has been developed which reduceshold-up volume and produces numerous other advantages when compared withprior art devices.

1. An apparatus for filtering fluid, the fluid being received into theapparatus from a fluid container placed in fluid communication with aninlet port on the apparatus, the fluid passing through a porous filterelement pinch sealed within the housing, and the filtered fluid exitingthe apparatus through an outlet port being in flow communication with afluid receiving container, said apparatus comprising: a. a housingcomprising: i. an inlet section having at least a portion of an inletchamber formed therein, and a passageway in fluid communication withsaid inlet chamber at one end thereof and with atmosphere at the otherend thereof; and ii. an outlet section having at least a portion of anoutlet chamber formed therein, and a passageway in fluid communicationwith said outlet chamber at one end thereof and with atmosphere at theother end thereof, bonded to said inlet section; and b. a porous filterelement pinch sealed between the inlet section and the outlet sectionwhen said outlet section and said inlet section are bonded together, andforming the remainder of said inlet chamber and said outlet chamber,wherein at least a portion of said porous filter element is chemicallytreated to modify the surface properties of the treated fibers onlypartway through a thickness of the porous filter element at the pinchseal between the inlet section and the outlet section, thereby causingthe porous filter element to be liquiphobic at least in a portion of itssealing region.
 2. A sheet of filter media having substantially parallelopposed surfaces and a sealing region proximate the edge of the filtermedia and between the substantially parallel opposed surfaces, thesealing region proximate the edge of the filter media having beenchemically treated to be liquiphobic or liquiphillic only partwaythrough a thickness of the filter media at the sealing region betweenthe substantially parallel opposed surfaces.
 3. A filter media of apredetermined shape having substantially parallel opposed surfacescomprising at least two regions with distinct media properties, one ofsaid at least two regions being chemically treated to modify the surfaceproperties of the fibers forming the filter media to cause said one ofsaid at least two regions to be liquiphobic or liquiphillic only partwaythrough the thickness of the filter media between the substantiallyparallel opposed surfaces.
 4. A filter media of a predetermined shapehaving substantially parallel opposed surfaces comprising at least tworegions with distinct media properties, one of said at least two regionsbeing chemically treated on its surface to be more or less hydrophobicor hydrophilic than the other of the at least two regions only partwaythrough the thickness of the filter media between the substantiallyparallel opposed surfaces.
 5. In combination a filter media having asealing region pinch sealed between two opposed surfaces in a filterhousing, and being of a predetermined shape comprising at least tworegions with distinct media properties, one of said at least two regionsbeing chemically treated to be hydrophobic in the sealing region,thereby resulting in enhanced sealing of the filter media in the filterhousing, the filter housing having an opposed pair of upstanding ridgesholding said media in a pinch seal, wherein each of said pair ofupstanding ridges is wider than the chemically treated region so air cannot pass through the sealing region.
 6. A filter media havingsubstantially parallel opposed surfaces of a predetermined shapecomprising at least two layers, each one of said at least two layershaving at least two substantially identical regions with distinct mediaproperties formed by chemical treatment of the surface of each of the atleast two layers only partway through the thickness of each one of saidat least two layers between the substantially parallel opposed surfaces,which results in enhanced sealing of said filter media between saidfilter media and a sealing means.
 7. A filter media of a predeterminedshape having substantially parallel opposed surfaces comprising at leasttwo layers, each one of said at least two layers having at least twosubstantially identical regions with distinct media properties formed bychemical treatment of the surface of each of the at least two layersonly partway through the thickness of each one of said at least twolayers between the substantially parallel opposed surfaces which resultin enhanced sealing of said filter media and a filter housing.
 8. Afilter media of a predetermined shape having substantially parallelopposed surfaces and comprising at least two layers, each one of said atleast two layers having at least two substantially identical regionswith distinct media properties formed by chemical treatment of each ofthe at least two layers only partway through the thickness of each oneof said at least two layers between the substantially parallel opposedsurfaces, which result in enhanced sealing of said filter media betweensaid filter media and a filter housing having an opposed pair ofupstanding ridges holding said filter media in a pinch seal, whereineach of the opposed pair of upstanding ridges is narrower than either ofthe at least two substantially identical regions so a gas can passthrough the substantially identical regions.
 9. A sheet of filter mediaof a predetermined shape having substantially parallel opposed surfacesand having an edge region and an annular treated portion of the sameshape as the predetermined shape spaced evenly and inwardly from theedge region, the annular treated portion formed by applying a liquidrepellant to the surface of the sheet of filter media.
 10. The filtermedia described in claim 9 wherein said liquid repellant in said annularregion extends part way through said sheet of filter media.
 11. Thefilter media described in claim 9, wherein said treated annular portionis in the form of an inwardly, radially extending U-shaped channel. 12.The filter media described in claim 9, wherein said treated annularportion is in the form of an outwardly, radially extending U-shapedchannel.
 13. The filter media described in claim 9, wherein said treatedannular portion is in the form of a box channel.
 14. In combination, thefilter media defined in claim 9 mounted in the filter housing defined inclaim
 1. 15. A flat sheet of filter media of a predetermined shapehaving an edge region; and a. an annular shaped portion, the entireannular shaped portion proximate said edge region and treated onlypartway through a thickness of the sheet of filter media with a liquidrepellant on each side of said flat sheet of filter media to form afirst annular liquid repellant portion and a second annular liquidrepellant portion.
 16. The filter media described in claim 15 whereinsaid treated annular portion is in the form of an inwardly, radiallyextending U-shaped channel.
 17. The filter media described in claim 15wherein said treated annular portion is in the form of an outwardly,radially extending U-shaped channel.
 18. The filter media described inclaim 15 wherein said treated annular portion is in the form of a boxchannel.
 19. A flat sheet of filter media of a predetermined shapehaving an edge region; and a. an annular shaped portion complimentary inshape to the predetermined shape, the entire annular shaped portionspaced a predetermined distance inwardly from said edge region andtreated with a liquid repellant to lower the surface tension of saidannular region.
 20. A sheet of filter media of a predetermined shapehaving an edge region: a. an annular shaped portion proximate said edgeregion treated with a liquid repellant to lower the surface tension ofsaid annular region, said annular shaped portion further including, i. afilter vent proximate the bottom of said annular shaped portion, whereinsaid sheet of filter media is circular in shape, said filter vent issemi-circular in shape, is integral with, and extends beyond the innerdiameter of annular shaped portion.
 21. A sheet of filter media of apredetermined shape having an edge region: a. an annular shaped portionspaced inwardly a predetermined distance from said edge region treatedwith a liquid repellant to lower the surface tension of said annularregion, said annular shaped portion further including; i. a filter ventproximate the bottom of said annular shaped portion, wherein said sheetof filter media is circular is shape, said filter vent is semi-circularin shape, is integral with, and extends beyond the inner diameter ofsaid annular shaped portion.
 22. A filter media having an annular liquidrepellant porous pinch sealing region spaced inwardly from the edge ofthe filter media, and a liquid wetting filter area on both sides of theannular pinch sealing region, wherein the filter media is a sheet, theannular liquid repellant porous sealing region is proximate the edge ofthe sheet, and extends only part way through the thickness of the sheet.23. The filter media defined in claim 22, with minimum fluid hold upvolume within the filter media.
 24. A filter media of a predeterminedshape having a filtering region and a pinch seal region, wherein thepinch seal region or the filtering region is treated only part waythrough the thickness of the filter media to provide differentialwetability of the filter media surface in the pinch seal region in theradial direction of the filter media.
 25. A liquid wetting filter mediaof a predetermined shape comprising at least two regions with distinctmedia properties, one of the at least two regions being a filteringregion, and at least one of the other at least two regions being a pinchseal region, wherein the pinch seal region is treated only part waythrough the thickness of the liquid wetting filter media to produce afilter media having liquid repellant porous pinch seal region with aliquid wetting filter area while filtering a liquid.
 26. An apparatusfor filtering fluid, the fluid being received into the apparatus from afluid container placed in fluid communication with an inlet port on theapparatus, the fluid passing through a flat porous filter elementcontained within the housing, and the filtered fluid exiting theapparatus through an outlet port in flow communication with a fluidreceiving container, said apparatus comprising: a. A housing comprising:i. an inlet section having at least a portion of an inlet chamber formedtherein, and a passageway in fluid communication with said inlet chamberat one end thereof, and with atmosphere at the other end thereof, and adownstanding peripheral ridge to seal a filter media; ii. an outletsection having at least a portion of an outlet chamber formed therein,and a passageway in fluid communication with said outlet chamber at oneend thereof, and with atmosphere at the other end thereof, bonded tosaid inlet section, and an upstanding peripheral ridge to seal a filtermedia; and b. a filter element pinch sealed between the downstandingperipheral ridge of the inlet section and the upstanding peripheralridge of the outlet section when said outlet section and said inletsection are bonded together, and forming the remainder of said inletchamber and said outlet chamber, wherein at least a portion of saidfilter element is chemically treated only part way through the thicknessof the filter element to be liquiphobic at least proximate theupstanding and downstanding peripheral ridges.
 27. A sheet of filtermedia having a region proximate the edge of the filter media, the regionproximate the edge of the filter media having been chemically treatedonly part way through the thickness of the sheet of filter media to beliquiphobic.